The present invention relates generally to automotive electrical power systems, and more particularly, to a method and apparatus of adaptive fusing within an electrical circuit.
Various types of multi-voltage level on-board systems have been proposed for automobiles. Typically, the automotive electrical systems use 14 volts. Recently, however, the automotive industry has started to discuss moving to a higher system voltage, such as 42 volts. A higher voltage system is particularly adapted to supply power to high power loads, such as the integrated starter alternator of the vehicle. The use of higher voltages allow the use of lower current for existing electrical loads, and allowing more power to be available for other loads.
Higher voltage systems create increased arcing between switch contacts and terminals upon separation. The severity of the arc increases drastically with increase in voltage. Various drawbacks may also be evident.
In 42-Volt systems, when electrical contacts are separated or brought close together an electrical arc may occur between the contacts, which has a sparl/arc intensity and temperature much more severe as compared with the present 14-Volt systems. Unfortunately, present passive fusing schemes, such as in-line fuses, only protect against an over-current condition and not against most common series or parallel faults caused by arcing between contacts. For example, in the case of loads such as motors and lamps, the fuse element is usually oversized so as to be capable of withstanding the large inrush currents, which is pre-selected based on the usage profiles of these loads. In-line fuses therefore are incapable of protecting against short circuits of very small duration (slow blow) or resistive shorts that do not significantly exceed usual 350% rated current of the fuse to blow quickly, thereby overstressing circuit wires.
Recently, there has been an introduction of an Arc Fault Circuit Interrupter (AFCI), as in U.S. Pat. Nos. 5,835,321 and 5,121,282, based on the detection of a high frequency signal seen during a sustained arc during a showering arc (amplitude varying arc having different frequency components). The frequency detection could be problematic, especially in the case of arcing with inductive or capacitive elements in series, due to filtering of these high frequencies, depending on the location of the arc (after the load). However, for vehicle applications the detection and filtering system is so coarse that the AFCI could falsely trip. A false trip occurs when a fusing technique falsely interrupts current in an electrical circuit when a normal increase in current level occurs for a brief period of time during normal operation. U.S. Pat. No. 5,839,092 looks at rate-of-change of current and polarity in household AC-systems. The system described in patent xe2x80x3092 does not consider duration of the arcs, which is therefore inapplicable for vehicle environments having various components with various normal operating characteristics. During normal operation insignificant arcs may occur, which would cause the patent xe2x80x3092 to interrupt the current. For example, in the case of the main battery supply, a false trip of the fuse would cause the vehicle to loose power.
Therefore, it is desirable to develop a new technique for electrical current interruption. The new technique should be capable of interrupting a circuit during an arc fault while minimizing false tripping. Additionally, the new technique should be capable of adapting to load conditions that it is being used to protect.
The forgoing and other advantages are provided by a method and apparatus of adaptive fusing for an electrical circuit. An adaptive fusing electrical circuit including a power supply and an electrical load drawing an electrical current therethrough. The circuit includes a current detector that measures a current level through the circuit. An interruption switch, which is normally closed, is electrically coupled to the electrical load and the current detector having an open state and a closed state. A controller is coupled to the power supply, the current detector, and the switch. The controller monitors the current level and a first circuit parameter of the circuit. The controller has a first guard band corresponding to the current level and a second guard band corresponding to the first circuit parameter. The controller compares the current level to the first guard band and the first circuit parameter to the second guard band. The controller interrupts the electrical current by switching the interruption switch from the closed state to the open state when the current level is outside the first guard band and the first circuit parameter is outside the second guard band.
The present invention has several advantages over existing fusing techniques. One advantage of the present invention is that it provides an improved and reliable adaptive fusing technique. The present invention also interrupts the circuit during an arc fault while minimizing false tripping.
Another advantage of the present invention is that it is capable of adapting to the load conditions that it is being used to protect. In other words, the present invention adapts to aging effect of loads by monitoring current decay rates during normal operating conditions.
The present invention itself, together with further objects and attendant advantages, will be best understood by reference to the following detailed description, taken in conjunction with the accompanying drawing.